This invention relates generally to a cellular telephone and more particularly is concerned with providing protection relating to the use of a battery with a cellular telephone.
In general, cellular telephones are not permitted to be used in hazardous locations such as petrochemical refineries, mines, or any environment in which gas, vapours, solvents, flying fibres and dust are present for there is a risk that the telephone, or its battery, could create an arc or a spark which could cause an explosion.
A spark could arise in a number of ways. For example an incorrect battery could be connected to a cellular telephone and, in use, the battery could become excessively hot, provide an over-voltage or over-current, or some other factor could arise which generates a spark. The problem is compounded in that printed circuit boards which are used with cellular telephones are, in their nature, of compact construction with very small track width and minimal track separation.
Any possible short circuit condition is of particular importance. A typical lithium ion battery can produce as much 30 Amps on a short circuit condition and this can destroy the entire battery. Although it is known to make use of a protection integrated circuit in a battery pack this type of circuit limits the amount of charge and discharge current but does not provide sufficient protection against abnormal conditions which can destroy the protection integrated circuit.
Another potential problem can arise when the battery is recharged. If the temperature of the charger increases, for whatever reason, above a predetermined level unwanted effects can occur which can give rise to the generation of a spark.
In the light of problems of the aforegoing type, and as a general rule, the use of a cellular telephone in a hazardous location is not permitted.